Physical chemistry chemical physics : PCCP

Photodissociation dynamics of SOCl2.

PMID 19785152


New theoretical and experimental results for the ultraviolet photodissociation dynamics of thionyl chloride (SOCl2) are presented and combined with existing data from a variety of sources in order to provide a unified view of the photodissociation dynamics of SOC12. Time-dependent density functional theory on the basis of the hybrid-type B3LYP functional was employed to calculate vertical excitation energies for the SOCl2 parent molecule up to 6.3 eV. Three-dimensional (3D) imaging of photofragments was performed for a dissociation wavelength of 235 nm. Atomic chlorine fragments were observed in the 2P(3/2) ground state [Cl] and the 2P(1/2) excited spin-orbit state [Cl*] by employing resonance enhanced multi-photon ionization (REMPI) and time-of-flight (TOF) techniques. State-specific speed distributions and the speed dependence of the beta anisotropy parameter were obtained from the full 3D momentum vector distribution by appropriate projection methods. Bimodal speed distributions for both spin-orbit states are evidence of a competition between the radical (SOCl2 --> SOCl + Cl/Cl*) and the three-body decay channel (SOCl2 --> SO + 2 Cl/Cl*). No evidence of the molecular fragmentation channel (SOCl2 --> SO + Cl2) was found. With increasing fragment speed the beta anisotropy parameter increases from 0.1 to 0.85 and 0.68 for Cl and Cl*, respectively, suggesting fragmentation via an excited A' state for slow fragments and via an A" state for fast fragments. The calculations allow for the first time to interpret all previous and new experimental data for the ultraviolet photodissociation of SOCl2 by assuming simultaneous excitation of several excited electronic states giving rise to competing dissociation channels.